Extractive fractionation pbocess



March 11, 1952 c. FETTERLY 2,588,506

EXTRACTIVE FRACTIONATION PROCESS Filed April l5, 1947 Patented Mar. 11, 1952 UNITED STATES PATENT OFFICE EXTRACTIVE FRACTIONAT'ION PROCESS Lloyd C. Fetterly, Long Beach, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application April 15, 1947, Serial No. 741,677

Claims.

This invention relates to a process for the extractive fractionation of organic compounds. More particularly, it relates to improvements in the process of fractionally extracting organic compounds from mixtures thereof by the useof vsuch complex-forming agents as urea and thiourea.

The fractionation of mixtures of organic compounds. presents complicated problems, both technical and economic. For example, the separation of mixtures of closely allied isomers, such as octane from iso-octane, is difficult by any of the more reasonably economic procedures, such as fractional distillation. Further, efliciency of. conversion4 procedures such as alkylation, isomer-ization and cycli'zation reduced if feed stocks. are not of the correct composition, either during the primary feed state or in recycling operations.

Ln most. of' such. conversion reactions an equi- Iibrium mixture isv generally obtainedv comprising fixed ratios of unconverted feed stock and the desired product. If the feed. stock initially contains some of the conversion product, .such as from a previous cycle through the converter, the amount of conversion is correspondingly reduced.

The two principal means for fractionation of such mixtureson a commercial scale have been by fractional distillation and by solvent extraction. Recently, however, a new method has been shown to be .suitable for large. scale separations, namely extractive crystallization with urea. It was found that urea forms crystalline complexes withorganic compounds of substantially straighty Mixtures of these complex-forming agents have been employed to extract normal and branched non-aromatic compounds as well as naphthenes from mixtures containing other types of compounds usually in excess. This latter process is usually employed for the purication of aromatics such as benzene, toluene, etc;

These processes are particularly applicable to the refinement of petroleum or other hydrocarbon mixtures, especially those of normal structure (which may be suitably fractionated 'by complex formation with urea) or hydrocarbons of branched chain or saturated cyclic structure (which readily form complexes with thiourea). The general procedure known to the prior art. comprised treatment of' such `mixtures with a solution of the ycomplex-forming agent. Under these circumstances a mixture of complexes usually was formed. This was due to the characteristics of the complex-forming agentsJ whereby under a given set of operating conditions certain classes of compounds formed complexes with the agents present. Thus, if both isoparaiiins and naphthenes were present in a mixture of hydrocarbons, the treatment of such a mixture with thiourea resulted in the formation of' complexes of both of these types of. hydrocarbons with thiourea. For many purposes the presence of one ,or another type of compound in admixture with other types, is undesirable. If, for example, this process were being used Vfor the preparation of high. octane gasoline, the

presence oflnaphthenes in the product would. be

chain structure, while ity appears to. be inert insthis respect toward branched compoundsv such. i

as the isoparaiiins, or cyclic compounds such` as most aromatics and naphthenes. The complexes. so formed are of indeterminate structure, but appear to be unstable molecular complexes rather than true chemicalv reaction products. This is indicated by their unstable character and the consequent ease of the regeneration of their components, namely urea and the unaltered organic compound.

When thiourea is the complex-forming, agent employed lthe complexes formed, thereby are usually of a substantially different character `in that thiourea forms complexes with organic compounds having either a branched configura tion or a cycloaliphatic structure. Under normal operating conditions thiourea forms only minor amounts of complexes with organic Vcompounds or normal 'structuragsuch as the normal paraiiins;

undesirable. Therefore, an improvement upon the known process would comprise a revision thereof whereby the final product substantially excluded naphthenes and largely comprised isoparaflins.

In a number of `instances a mixture of organic compounds contains a relatively minor fraction of material which will form crystalline complexes with one of theV above agents. It has been noted that if only a minor amount of complexes are formed and thereafter separated from the mixture by filtration the thin layer of crystals tends to clogr the lter cloth and thus to reduce the eiiciency of the filtration step.

It is an object of this invention to improve either urea or thiourea. It is another object of this invention, to provide for the production of more highly fractionatedk materials than those J heretofore possible. byk the subjectfextractive fractionation processes. It is a further object of this invention to improve the efficiency of the.

separation step, avoiding the clogging of filters. Other objects will become apparent during the following discussion.

Now, in accordance with this invention, it has been found that the fractionation of mixtures of organic compounds by the subject extractive fractionation processes may be improved by recycling part of the raffinate separated from the complexes formed as described above. Still in accordance with this invention, it has been found that further improvements may be effected by subjecting the rafnate toj conversion processes and thereafter fractionating the product and returning a portion thereof to the original mixture of organic compounds. By raiiinate" is meant that portion of the original mixture of organic compounds not forming complexes with the complex-forming agent. By conversion processes is meant a process wherein the raffinate is substantially changed by such means as alkylation, isomerization, hydrogenation, or by the formation of other complexes. I

g In carrying out the process of the present invention, mixtures of organic compounds are contacted with a complex-forming agent (suitably either urea or thiourea) and passed to a separator wherein the complexes are separated from the raffinate. Following isolation of the rafnate,

the process according to the present invention comprises one of two alternative steps: either the fractionation of the raffinate or the conversion thereof. The fractionation of the raflinate may take place by any of the well known means such as distillation, solvent extraction, or extractive fractionation with a complex-forming agent other than the one originally employed. By carrying out this fractionation the raffinate is separated into portions having desired configurations or properties, at least one of said portions being so i.

constituted as to enrich the original mixture of organic compounds when recycled thereto. For example, under normal operating conditions an equilibrium exists in any extractive fractionation process. If the original mixture of organic compounds contains a relatively small amount of compounds capable of forming complexes with either urea or thiourea as the case may be, only a minor amount of complex formation will occur and most of the potentially active organic com- 1 pound remains in the raflinate. If, however, the latter is treated with a complex-,forming agent removing a constituent thereof which was inert toward the complex-forming agent first employed,

then the original desired fraction is concentrated and may be returned to the feed.

The efficiency of conversion operations such as isomerization is limited by similar equilibrium phenomena. For example, if the feed in an isomerizer contains isomerized material the degree of isomerization taking place is reduced to a corresponding extent. In order to improve the efficiency of such reactions it is highly desirable to remove from the feed any isomerized material prior to subjecting such feed to isomerization. Consequently, the process of the present invention comprises a means whereby the eciency of conversion operations may be improved according to the following scheme: the feed for an isomerizer is subjected to extractive fractionation with a complex-forming agent after which the complexes are removed vand the raffinate is subjected to an isomerization treatment. The resulting product is fractionated as well as Dossible by distillation and then the fraction thereof containing minor amounts of the isomerized product and major amounts 0f a fraction undesirable in the isomerizer is returned to the original feed and subjected to the action of complexforming agents. The raffinate resulting from such an operation consequently has a reduced amount of product undesirable in the isomerizer. A specific case in point is that of the preparation of high anti-knock gasoline by a combined process of fractional extraction and isomerization. A gasoline having relatively low anti-knock value is subjected to the action of thiourea whereby the branched hydrocarbons having high anti-knock values are removed from the original mixture leaving a feed substantially comprising hydrocarbons of straight-chain configuration as a raffinate. This raiiinate is then subjected to an isomerization reaction whereby a portion thereof is converted to branched hydrocarbons having improved anti-knock values. The resultingmixture is fractionated by distillation into the portions having high anti-knock value and another portion having unconverted normal hydrocarbons in admixture with a minor amount of branched hydrocarbons. This latter fraction is returned to the original extractive vessel together with additional quantities of the original gasoline so that the branched hydrocarbons may be removed and the raiiinate of normal structure again subjected to isomerization.l By the process of this invention as described above, isomerized material is substantially removed from the isomerization feed thus improving the efficiency of the isomerization reaction. Similar processes may be readily designed for the improvement of other conversion operations.

` With reference to the drawing which comprises a flow diagram for the fractional extraction of mixtures of organic compounds in accordance Vwith the method of the present invention, said compounds are contacted in the mixer l with a complex-forming agent, namely urea or thiourea; the resulting slurry of crystalline complexes and unconverted rafnate is conducted to the separator 2 which may be a rotary drum filter, centrifuge, or other separating means wherein the crystalline complexes are separated from the ramnate. The complexes are then passed on to .the regenerator 3 wherein the constituent parts, namely the complex-forming agent and the organic compounds forming complexes therewith are regenerated. The raffinate passes from the separator directly to the fractionator 5 through by-pass line 6 or alternatively to the convertor 4. The conversion step has been described above as comprising isomerization, alkylation, etc. If such conversion is employed the product thereof is conducted to the fractionator 5 wherein the product is separatedinto one portion with which it is desired to enrich the original feed. This portion is returned to the mixer I.

The mixtures of organic compounds whichmay be treated with urea by the process of the pres:- ent invention comprise compounds having substantially normal structure and/or compounds having a predominating substituent of substantialy normal structure. Conditions may be employed whereby certain normal organic compounds are separated from other normal organic compounds, or from other organic compounds such as isoparaiiins, aromatics, naphthenes, etc. The organic compounds of normal structure which may be formed into complexes by theproc-y ess of the present inventioninclude bothsaturated and unsaturated compounds, especially the parailins, varrdl olens; The normall compounds' maybeof a number of types, sucha's hydrocarbons, alcohols, kei-onesI aldehydes, kesters;amines, amides, suldes, disuldes, mercaptans,. acids; halogenated compounds, others, nitro-compounds, silicones, carbohydrates, etc. The hydrocarbons respond especially well to the` 'processi of the presentinvention.

Suitable hydrocarbons which form crystalline complexes with urea include the paraflinic hydrocarbons such as butane, pentane, hexane,V heptane, octane, nonane, decane, undecane, dodec'ane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, etc.

Olefin .hydrocarbons which may be. treated by the process of the present invention-include' l-butene, 2-butene', l-penten'e, 2-pentene, l-hexene, 2-hexene, 3-hexene, l-heptene, 2-heptene, 3-heptene', 1octene, 2octene, 3-octene, 4-octene', 2nonene, 3-nonene, 4-nonene, l-decene', 2-decene, 3-decene, 5decene, l-undecene, 2unde cene, 5-undecene, l-dodecene', 6dodecene, l-tridecene, `G-tridecene, l-pentadecene, S-heptadecene, 13-heptacosene, etc.

Another class of hydrocarbons which may be formed into complexes with urea, according to the process of the present invention are the normal diolens such as 1,2-butadiene, 1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, 1,4-pentadiene, 1,2-hexadiene, 1,3-hexadiene, 1,4-hexadiene, 1,5-hexadene, 2,3-hexadiene, 2,4-hexadiene, 1,3-heptadiene, 1,6-heptadiene, 2,4-heptadiene, 1,4-octadiene, 1,5-octadiene, 1,7-octadiene, f

2,6-octadiene, 3,5-octadiene, 1.5-nonadiene, 1,8-

nonadiene, 2,6-nonadiene, 1,3-decadiene, lai-decadiene, 1,9-decadiene, 2,8-decadiene, 3,7-decadiene, 2,6-dodecadiene, 1,17-octadecadiene, etc.

Normal hydrocarbons of a greater degreev of unsaturation which form crystalline' complexes with urea by the process of the" present invention include the triolenes, acetylenes, diacetylenes, olen-acetylenes and the diolen-acetylenes, including-1,3,5-hexatriene, 1,3,5-heptatriene, 2,3,6- octatriene, ethylacetylene, propylacetylene, butylacetylene, amylacetylene, caprylidene, 4-octyne, diacetylene, propyl-diacetylene, 1,8-nonadiyne, l-hepten-S-yne, 1,5-hexadien-3-yne, etc. Normal alcohols, especially those having six .or more carbon atoms, may be treated by the present process to form complexes with urea. These include the aliphatic monohydric alcohols such as hexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, decyl alcohol, dodecyl alcohol, cetyl alcohol, carnaubyl alcohol, and the polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and hexitol.

Ethers of normal structure forming complexes" with urea include acetal, dioxane, paraldehyde, crotonyl ether, etc. Aldehydes of normal struc-- ture also respond to the process of this invention, including butyraldehyde, valeraldehyde, c aproaldehyde, palmitic aldehyde, citral adipaldehyde. etc. Ketones which form urea complexes are exemplified by S-hexanone, palmitone, 2,3- pentanedione, etc. Acids also may be treated according to the subject process. Typical normal acids forming urea complexes are the normal fatty acids, especially those having four or lmore carbon atoms, such as butyric, valerio, caproic, enanthy1ic,'caprylic, pelargonic, capric, undecylic, lauric, tridecoic, myristic, pentadecanoic, palmitic, margaric, stearic, etc., acid. Acrylic acids also respond, such as methylacrylic acid, tiglic acid,v oleic acid,` etc. The acetylene acidsform 'urea complexes.y Thes'e include :sorbic4 and;

linoleic acids;

Other: types of normal-structured compounds which may be treated accordingto the processiof the presentv inventionV include esters; lsuch as amyl acetate, ethyl stearate, etc.; amines such as'n.- de'cyl amine, dibutyl amine and triethyl amine; amides, such as stearamide; mercaptans,.such as heptyl mercaptan; and other organic compounds of normal structure, including halogenated' derivatives of the above compounds, thioalcohols, alkyl hydrazines, thioaldehydes, amino acids, nitroparains, etc.

The mixtures containing the organicv compounds of" normal structure may be composed solely lof mixed normal compounds', or vthey may. contain materials substantially inert toward urea, such as branched para'ns, isoolens, aromatics,v cycloparains, etc, Usually, especially when treating natural products such as lpetroleum, the inert ingredients are present as isomers of the normal structure compounds, and may occur therewith naturally or by reason ofv some; treatment to which `the organic material has been subjected, such as alkylation, cyclization, isomer.- ization, etc. However, active or inert diluents or solvents may be added to normal organic compounds in order to modify the type and degree of crystallization of the latter with urea. The reason for and use of diluents is discussed here-- inafter.

Hydrocarbons which form complexes with thiourea are those having a predominating member which is a substantially branched radical or anaphthene radical, such as alkaryl hydrocar-fbons wherein at least one alkyl group is. an isoparailin radical of abouty six or more: carbon. atoms.

Isoparailins which form-complexes with thiourea.

include isobutane, isooentane. 2,2-dimethylpropane, isohexane, 2,3-dimethylbutane. 2-methylpentane, B-methylpentane, 2-ethylbutane, 2- ethylpropane, 1,1-dirnethylpentane, 1,2-dimethylpentane, 1,3 dimethylpentane, 1,4 dimethylpentane, 2-ethylpentane, 3ethylpentane, 2-npropylbutane, 2isopropylbutane, 2-methylhexane, 3rnethylhexane, 2,2-dimethylpentane, 2,3- dimethvlpentane, 2,4-dimethylpentane, 3,3-dimethylpentane. 2,2,S-trimethylbutane, Z-methylheptane, S-methylheptane, 4-methylheptane, 3- ethylhexane, 2,2-dimethylhexane, 2,3-dimethylhexane, 2.4-dimethylhexane, 2.5-di1nethylhexane, 3,3-dimethylhexane, 3,4-dimethylhexane; 2,2,3-trimethylpentane', 2,2,4-trimethylpentane,

` 2,3,3-trimethylpentane, 2,3,4 trimethylpentane',

2,2,3,3-tetramethylbutane, 2-methy1-3-ethylpentane, S-methyl-S-ethylpentane, 2-methyloctane`.- 3-methyloctane, 4-methyloctane, 2,2-dimethylheptane, 2,3-dimethylheptane, 2,4-dimethylheptane, 2,4-dimethylheptane, 2,5-dimethylheptane, 2,6-dimethylheptane, 3,3-dimethylheptane, 3,4- dimethylbeptane, 3 -ethylheptane, 4-ethy'lhep'- tane, 2,2,3-trimethylhexane, 2,2,4-trimethylhexane, 2,2,5-triinethylhexane, 2,2,5-trirnethylhexane, 2,3.3-trimethylhexane, 2,3,5-trimethylhex'- ane, 2,4,4-trirnethylhexane, 3,3,4-trimethylhexane, 21ncethyl3ethylhexane, 2-methyl-4-ethyl hexane; 2,2,3,S-tetrarnethylpentane, 2,2,3,3tetra methylpentane, 3,3 diethylpentane, 2,2' 'd`i` methyl-S-ethylpenta'ne, 2,3-dimethyl 3` ethylpentane, 2,4-dimethyl 3 ethylpentane, 2,253,4- tetramethylpentane, 2methylnonane, VS-'methylnonane, l-methylnonane,l 5methylnonane, .2,2- dimethyloctane, 2,3 dimethyloctane, 2,4 dimethyloctane. -2',5dimethyloctane, l2,6-d'imeth5`floctane, 2,7-dimethyloctane, 3,3-dimethyloctane, 3,4-dimethyloctane, 3,6-dimethyloctane, 4,5-dimethyloctane, 3-ethyloctane, 2,2,3-trimethylheptane, 2,3,3-trimethylheptane, 2,2,6-trimethylheptane, 2,3,6-trimethylheptane, 2.4,4-trimethylheptane, 2,4,6 -trimethylheptane, 3,3,5 -trimethylheptane, S-methyl-S-ethylheptane, 4-propylheptane, 4-isopropylheptane, 2,2,3,3 tetramethylhexane, 2,2,3,4-tetramethylhexane, 2,2,5,5tetra 3,3,4,4 tetramethylhexane, 3,3 diethylhexane, 3,4-diethylhexane, 2,2,4-trimethylheptane, 2,2,4,5 tetramethylhexane, 2-methyl-5-ethylheptane, 4- methyldecane, -methyldecane, 2,3-dimethylnonane, 2,4-dimethy1nonane, 2,5-dimethylnonane, 2,6 dimethylnonane, 3,3 dimethylnonane, 4- ethylnonane, -ethylnonane, 2,3,7-trimethyloctane, 2,4,7-trimethyloctane; 2,2,3,3-tetramethylheptane, 2,2,4 trimethyloctane, 2,2,4,6 tetramethylheptane, 2,2,4,5 tetramethylheptane, 3- methylundecane, 4 methylundecane, 2,3 dimethyldecane, 2,5 dimethyldecane, 2,6 dimethyldecane, 2,9-dimethyldecane, S-ethyldecane, 5 propylnonane, 2,2,7,7 tetramethyloctane, 2,3,6,7 tetramethyloctane, 2,4,5,7 tetramethyloctane, 3,3,6,6 tetramethyloctane, 2- methyl--propyloctane, 3,6-diethyloctane, 2,6- dimethyl-3-isopropylheptane, 4,5-diethyloctane, 2,2,4,6,6 pentamethylheptane, 2,2,4,4,6 pentamethylheptane, 5 methyldodecane, 2,10 dimethylundecane, 2,5,9-trimethyldecane, 4-propyldecane, 4-ethylundecane, 5-butylnonane, 2,11- dimethyldodecane, 4,5 -diisopropyloctane, 2,7- dimethyl4,5 diethyloctane, 4 propylundecane, 2,"I-dimethyl-4-isobutyloctane, 2,6,10-trimethyldodecane, 2,6,11-trimethyldodecane, -methyl-lethyldodecane, 5-propyldodecane 6-propyldodecane, 4-methy1--propylundecane, 6,9-dimethyltetradecane, 7,8-dimethyltetradecane, 3-ethyltetradecane, 5,7-diethyldodecane, 2,6,7,11-tetramethyldodecane, 4,7 dipropyldecane, 2,2,3,3,6,6, '7,7-octamethyloctane, 3,12 diethyltetradecane, 2,6,11 trimethyl 9 isobutyldodecane, 2,6-dimethyloctadecane, 5,7,9-triethyltetradecane, 2-

methyl-4-isobutylhexadecane, 2,9-dimethyl, 5,6- .l

diisoamyldecane, 4,8,13,17 tetramethylicosane, 2,11dimethyl5,-diisoamyldodecane, l-nonylnonadecane, 2,6,10,14,18,22 hexamethyltetracosane, 2,6,12,16tetramethyl9(2,6-dimethyloctyl) heptadecane, etc.

As stated hereinbefore another type of hydrocarbon which readily forms complexes with thiourea is that of the naphthenes. Typical species of this group include cyclopropane, methylcyclopropane, 1,1 dimethylcyclopropane, 1,2-dimethylpropane, ethylcyclopropane, 1,1,2- trimethylcyclopropane, 1,2,3 trimethylcyclopropane, 1-methyl-2-ethylcyclopropane, propylcyclopropane, 1-methyl-2-propylcyclopropane, cyclobutane, methylcyclobutane, ethylcyclobutane, 1,2- dimethylcyclobutane, propylcyclobutane, isopropylcyclobutane, 1,2diisopropy1cyclobutane. 1,2- dmethyl 3,4 diethylcyclobutane, 1,1,2,2tetra methyl-3,4diisopropylcyc1obutane, cyclopentane, methylcyclopentane, 1,1 dimethylcyclopentane, 1,2-dimethylcyclopentane, 1,3-dimethylcyclopentane, ethylcyclopentane, propylcyclopentane, isopropylcyclopentane, 1,1,3-trimethy1cyclopentane. 1-methyl-Z-ethylcyclopentane, l-methyl-S-ethylcyclopentane, lbutylcyclopentane, isobutylcyclopentane, 1 methyl 2 propylcyclopentane, 1- methyl-3-propy1cyc1opentane, 1,3 dimethyl- 2- ethylcyclopentane, 1,3 dimethyl- 5 ethylcyclopentane, 1,1-diethy1cyclopentane, amylcyclopentane. Visoamylcyclopentane, 2-cyclopentylpentane, 1-methyl-3-butylcyclopentane,V l-methyl- 2,5-'diethylcyclopentane, 1,2,3-trimethyl 4 -isopropylcyclopentane, heptylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, 1,1-dimethylcyclohexane, 1.2 dimethylcyclohexane, 1,3-dimethylcyclohexane, 1,2,3 -trimethylcyclohexane, 1,3,-trimethylcyclohexane, butylcyclohexane, l-methyl 4 ethylcyclohexane, 1- methyl-3-propylcyclohexane, 1 methyl 3 isopropylcyclohexane, 1,3-dimethyl-5 ethylcyclohexane, 1,3-diethylcyclohexane, amylcyclohexane, pentamethylcyclohexane, 1,2-dimethyl-3,6 diethylcyclohexane, 4-cyclohexylheptane, 3-cyclohexy1-3ethy1pentane, triisopropylcyclohexane, 2,8-dimethyl 5 ethyl- 5 cyclohexylnonane, 1- methyl-4 -isopropyl- 2 dodecyclohexane, octadecylcyclohexane, propylcycloheptane, etc.

The ratio of the complex forming agent to active organic compounds will vary with the type of mixture to be treated and with the conditions of complex formation. For example, the extractive fractionation may be carried out with the intention of removing from the mixture the maximum amount possible of the compounds of normal structures present. In this particular case, it is preferred practice to contact the mixture with urea employed in an amount in excess of that necessary for complete complex formation.

Complexes may be formed having varying amounts of the complex-forming agent combined with the active organic compound. When the temperature or other conditions during complex formation are such that about 3 mols of the agent combined with about every 4 carbon atoms of the active organic compound, it is preferred practice to contact the active organic compound with an amount of the agent somewhat in excess of this ratio.

The formation, separation and purification of the complexes having been accomplished as described hereinbefore, there remains the step of decomposing the complexes in order to recover the active organic compounds present therein. While a number of methods have been found for effecting such a decomposition or regeneration, the following methods have been found to be the most satisfactory for use when carrying out the process of the present invention:

A. Simple distillation.

B. Steam distillation.

C. Application of a solvent for the complexforming agent.

D. Heating.

E. Application of a solvent for a particular fraction of the regenerated organic compounds.

The complexes, as has been pointed out hereinbefore, are relatively unstable formations which appear to be loose combinations involving hydrogen bonding or some form of molecular attraction, the exact nature of which has not been deduced. It has been found that due to their unstable character, splitting into the component parts of the complex may be readily accomplished, the complex-forming agent and the organic compounds in complex combination therewith separately recovered in their original state.

By subjecting the complexes to distillation simultaneous destruction of the complex and fractionation of the organic compounds regenerated therefrom may be accomplished. The distillation may take place under normal or reduced pressures and the` temperature and pressure are so adjusted that the complexes are readily destroyed and the compounds regenerated therefrom are distilled into fractions which can be utilized for 9 the purposes considered herein. For example, if it is desired to enrich. the feed with low boiling normal hydrocarbons, complexes of urea and a mixture of normal hydrocarbons may be decomposed by distillation and the distillant may be recycled to the mixer.v

Steam distillation is a refinement of the above processv and the principle of regeneration and fractionation applies here as well. Steam distillation is preferable where the organic compounds to be regenerated are of such high boiling point that their distillation would be accomplished by substantial decomposition.

Avfurther type of regenerationcomprises addition of a solvent for the complex-forming agent such as water or alcohol to the complex and the application of heat to facilitate the regeneration. By this means the regenerated organic` compounds'l separate from the solution of the complex-'forming agent and subsequently may .be fractionated by normal purification or fractionation procedures.

A more preferred type ofregeneration comprises the addition of a solvent for one or more fractions of the organic compounds to be regenerated from the complexes. When such a Vmixture is heated Athe complex decomposes, thus regenerating the organic compounds and complexforming agents and, in presence of -su'ch a solvent, a solution of part of the regenerated organic compounds which form and may be readily separated from the insoluble fractions which are present. Hence, vfractionation according to solubility may be readily accomplished.

Fractionation byv simple heating is satisfactory for some purposes. Following the regeneration by such means it is usually necessary to purify or fractionate the regenerated compounds and the regenerated complex-formingagent for further use.

The process of the present invention is useful for the Apreparation of high octane gasoline or high diesel index fuel as well as for the preparation of internal combustion vengine fuels having a narrow boiling range.

I cla-im `as my invention:

1; The process whichcomprisesicontacting an alcoholicsolution of thiourea-which a mixture of gasoline hydrocarbons containing a minor amount of iso-octane in admix'ture with substantially straight chain hydrocarbons, whereby complexes are formed between thiourea and iso-octane, separating the complexes-from the rafnate comprising the remaining Agasoline hydrocarbons, subjecting the rainate to an isomerization process, whereby a portion thereof is converted to branched chain hydrocarbon structure, separating said portion from the remaining raffinate and returning it to the original mixture of gasoline hydrocarbons.

2. The. extractive fractionation process which comprises treating mixtures of petroleum hydrocarbons with a -complex-forming agent selected from the group consisting of urea andthiourea, separating the complexes thus formed, between said agent with a fraction of the hydrocarbon mixture, from the rai'linate comprising the remaining fraction of the mixture, subjecting the raffinate to fractionation and returning'a fraction thereofrich in compounds. capable ofform'- ing complexes with said agent to enrich further portions of the original mixture.

3. The extractive fractionation process which comprises treating mixtures of petroleum hydrocarbons containing substantially straight chain hydrocarbons with va, complex-forming agent select'ed from the' group consisting of urea vand thiourea, vseparating the complexes thus form-ed, between `said-agent with a fraction of the hydrocarbon mixture, from the rafnate comprising the remaining fraction of the mixture, subjecting the raiinate to fractionation and returning a fraction `thereof rich in compounds capable of forming complexes with *said agent to enrich further portions of theoriginal mixture.

4. The extractive yfractionation process which comprises treating mixtures of petroleum hydro; carbons containing substantially straight chain hydrocarbons with urea, separating the complexes thus formed between urea and said -s-ubstantially straight chain hydrocarbons from the ranate comprising the remaining fraction of the petroleum hydrocarbons, subjectingthe ramnate to Yfractionation returning a Yfraction thereof rich in Ycompos-.nails capableV of forming complexes with said agent to enrich further portions of the original petroleum mixture;

'5. The extractive fractionation process which comprises treating mixtures of a petroleum prod'- uct containing branched' chain hydrocarbonsv withv a complex-forming agent selected from the group consisting of urea and thiourea, separating the complexes thus formed, between said agent with a fraction ofthe hydrocarbon mixture, from the raffinate comprising the remaining fraction of the mixturegsubjecting the rafl-Vv nate to fractionation and returning' a 'fraction thereof' rich inl compoundsl capable of' forming complexes'with said 'agent' to enrich further por'- formed between thiourea and said branched chain' hydrocarbons from the railnate comprising the remaining portion of the petroleum iprodu'ct, subjecting the raffinate to fractionation and' returning a fraction thereof rich in compounds capable of forming complexes with s'aijd agent to enrich furtherportions of the original petroleum product;

'7. The extractive fractionation process which comprises treating mixtures of organic com-V pounds with a complex-forming agent selected from the group consisting of rurea and thiourea, separating the complexes thus formed, between said agentv with a fraction of'said. mixture, from theralinate comprising the remaining fraction 0f themixture, subjecting. therainnate to an a1-.

kylation process, fractionating the resulting product" 'and returning aV fractionthereof to the original mixture of organic' compounds'. l

8. vThe extractive fractionation process which comprises treating mixturesV of organic" *compounds with a complex-forming agent selected from the grou-p consisting of urea and: thiourea, separating the complexes thus formed, between said agent With-'a fraction o f said mixture, fromj the raffinate comprising the remaining fraction ofthe mixturavsubjecting the' rainnate to an isomerization process,-fractiona'ting the'resulting productandreturningv a fraction thereof to=th`e original mixture of organic compounds.

A9. AThe extractive'fractionation process'w-hicn comprises treating mixtures of organic compounds with thiourea separating the complexes thus formed between thiourea and a fraction of said mixture from the raflnate comprising the remaining fraction of the mixture, subjecting the 1l raffinate to the action of urea whereby complexes are formed between a portion of the rainate and urea, removing said complexes and returning the remaining portion of the rainate to the original mixture of organic compounds.

10. In the process for the extractive fractionation of mixtures of organic compounds with a complex forming agent selected from the group consisting of urea and thiourea, whereby complexes of said agent with a fraction of said mixture separate and are removed from vthe raffinate comprising the remaining fraction of said original mixture, the improvement which comprises removing from said rafhnate a predetermined portion thereof and recycling the remaining portion of the raiiinate to a point prior to separation of said complexes.

11. The extractive fractionation process which comprises treating mixtures of organic compounds with a complex-forming agent selected from the group consisting of urea and thiourea, separating the complexes thus formed between said agent with a fraction of said mixture, from the rafnate comprising the remaining fraction mixture, subjecting the raffinate to a conversion operation, fractionating the conversion product thus formed'and returning a fraction thereof to the original mixture of organic compounds.

12. The extractive fractionation process which comprises treating mixtures of organic compounds with a complex-forming agent selected from the group consisting of urea and thiourea; separating the complexes thus formed, between said agent with a fraction of said mixture, from the raffinate comprising the remaining fraction of the mixture; subjecting the raffinate to fractionation and returning a fraction thereof rich in compounds capable of forming complexes with said agent to enrich further portions of the original mixture.

13. The process which comprises treating a feed comprising mixtures of petroleum distillates containing straight-chain hydrocarbons and branched-chain hydrocarbons with urea, separating crystalline complexes thus formed between urea and a portion of the straightchain hydrocarbons from a raflinate comprising branched-chain and unreacted hydrocarbons, contacting said ramnate with thiourea, separating crystalline complexes thus formed between thiourea and a, portion of the branched-chain hydrocarbons from a second raffinate comprising predominantly straight-chain and minor amounts of unreacted branched-chain hydrocarbons, and returning said second raffinate to further portionsof the original feed to enrich said feed, and subjecting the enriched feed to the first described urea fractionating operation.

14. The extractive fractionation process which comprises treating a mixture of organic compounds, some of which form solid complexes with urea and some of which form complexes with thiourea, with a, first complex-forming agent selected from the group consisting of urea and thiourea, under conditions to form solid complexes between said first agent and only a portion of the organic compounds present which are capable of forming solid complexes therewith, separating the solid complexes thus formed between said rst agent with a fraction of said mixture from a first raiiinate comprising the remaining fraction of the mixture, contacting said first raiiinate with a second complex-forming agent selected from the group consisting of urea and thiourea, which second agent is different from said first agent, separating the complexes thus formed between said second agent with a fraction of the first raffinate from a second raffinate comprising the remaining fraction of said first raiiinate, and returning said second raffinate to a further portion of the original mixture to enrich said mixture and subjecting it to the first abovedescribed complex formation step.

15. The process which comprises treating a feed comprising a petroleum distillate mixture containing straight-chain hydrocarbons and branched-chain hydrocarbons with thiourea under conditions to form solid complexes between said thiourea and only a portion of the branchedchain hydrocarbons, separating crystalline complexes thus formed between thiourea and a portion of the branched-chain hydrocarbons from a raiiinate comprising straight-chain hydrocarbons and uncomplexed branched-chain hydrocarbons, contacting said raiiinate with urea, separating crystalline complexes thus formed between urea and a portion of the straight-chain hydrocarbons from a second ralinate comprising predominantly branched-chain hydrocarbons and minor amounts of straight-chain hydrocarbons, and returning said second raffinate to a further portion of the original feed to enrich said feed, and subjecting the enriched feed to the first described thiourea fractionating operation.

LLOYD C. FETTERLY.

REFERENCES CITED file of this patent:

UNITED STATES PATENTS Number Name Date 2,109,895 Anderson Mar. 1, 1938 2,221,301 Kipper Nov. 12, 1940 2,246,257 Kohn June 17, 1941 2,260,279 DOuville et al Oct. 21, 1941 2,342,888 Nysewander et al. Feb. 29, 1944 2,374,102 Jahn et al Apr. 17, 1945 2,376,008 Riethof May 15, 1945 2,386,335 Morris Oct. 9, 1945 2,396,303 Cummings et al. Mar. 12, 1946 2,410,166 Kimball Oct. 29. 1946'- 2,423,414 Soday July l, 1947 FOREIGN PATENTS Number Country Date 459,189 Great Britain Jan. 4, 1937 OTHER REFERENCES Bengen: Technical Oil Mission Reel 6, P. B.

Berichte, vol. 7 (1874). Dp. 779-780 (article by Nencki).

Comptes Rendues, vol. 224 (1947), pp. 402-404 and pages 1166-1167 (articles by Angla.). 

10. IN THE PROCESS FOR THE EXTRACTIVE FRACTIONATION OF MIXTURES OF ORGANIC COMPOUNDS WITH A COMPLEX FORMING AGENT SELECTED FROM THE GROUP CONSISTING OF UREA AND THIOUREA, WHEREBY COMPLEXES OF SAID AGENT WITH A FRACTION OF SAID MIXTURE SEPARATE AND ARE REMOVED FROM THE RAFFINATE COMPRISING THE RAMAINING FRACTION OF SAID ORIGINAL MIXTURE, THE IMPROVEMENT WHICH COMPRISES REMOVING FROM SAID RAFFINATE A PREDETERMINED PORTION THEREOF AND RECYCLING THE REMAINING PORTION OF THE RAFFINATE TO A POINT PRIOR TO SEPARATION OF SAID COMPLEXES. 